In the case of HIV, we previously satisfied these conditions by spinoculating the highly permissive CEM-T4 lymphoblastoid T cell line (Foley et al., 1965; O'Doherty et al., 2000; Popovic et al., 1984) with Env-deficient NL4-3-ΔEnv-EGFP virus (Zhang et al., 2004) at a high multiplicity of infection (MOI) (Greenwood et al., 2016). Here, ERVW-1 is linked to infection.